Device and method for controlling a raster scanner in ion-beam therapy

Abstract

The invention relates to an apparatus and a method for the feedback control of a grid scanner in ion therapy. An apparatus of that kind for the feedback control of a grid scanner has scanner magnet current supply devices for ion beam scanner magnets that deflect horizontally and vertically with respect to the middle of the ion beam, the supply devices being controlled by control and read-out modules for the scanner magnets. Furthermore, the apparatus has a location-sensitive detector for location measurement, which is controlled by means of a control and read-out module. A sequence control device controls the activation and read-out sequence among the devices of the apparatus, the apparatus also having in the sequence control device a circuit arrangement having a feedback loop between the control and read-out modules for the scanner magnets and the control and read-out module of the location-sensitive detector. For that, the control and read-out modules for the scanner magnets and the control and read-out module of the location-sensitive detector in the sequence control device are technically so arranged, in circuitry and sequence, that the control and read-out modules for the scanner magnets are arranged serially after the control and read-out module of the location-sensitive detector.

What is claimed is:  
     
       1. Apparatus for the feedback control of a grid scanner in ion beam therapy, which has, at least, the following devices: 
       scanner magnet current supply devices (MGN) for ion beam scanner magnets that deflect horizontally (X) and vertically (Y) with respect to the middle of the ion beam, the supply devices (MGN) being controlled by control and read-out modules (SAMS) for the scanner magnets,  
       a location-sensitive detector (MWPC 1 ) for location measurement, which is controlled by means of a control and read-out module (SAMO 1 ),  
       a sequence control device (VMEAS), which controls the activation and read-out sequence among the devices of the apparatus,  
       characterized in that the apparatus 
       has in the sequence control device (VMEAS) a circuit arrangement having a feedback loop between the control and read-out modules (SAMS) for the scanner magnets and the control and read-out module (SAMO 1 ) of the location-sensitive detector (MWPC 1 ) and,  
       in circuitry and sequence, the control and read-out modules (SAMS) for the scanner magnets and the control and read-out module (SAMO 1 ) of the location-sensitive detector (MWPC 1 ) in the sequence control device (VMEAS) are technically so arranged that the control and read-out modules (SAMS) for the scanner magnets are arranged serially after the control and read-out module (SAMO 1 ) of the location-sensitive detector (MWPC 1 ).  
     
     
       2. Apparatus according to  claim 1 , characterized in that a multi-wire proportional chamber is used as the location-sensitive detector (MWPC 1 ). 
     
     
       3. Apparatus according to  claim 1  characterized in that it has at least one ionization chamber (IC 1 ) for measuring the intensity of the ion beam, the control and read-out module (SAMI 1 ) of which ionization chamber is, within the sequence control (VMEAS), technically arranged, in circuitry and sequence, before the control and read-out module (SAMO 1 ) of the location-sensitive detector (MWPC 1 ). 
     
     
       4. Method for the feedback control of a grid scanner in ion beam therapy, wherein the grid scanner has, at least, the following devices: 
       scanner magnet current supply devices (MGN) for ion beam scanner magnets that deflect horizontally (X) and vertically (Y) with respect to the middle of the ion beam, the supply devices (X, Y) being controlled by control and read-out modules (SAMS) for the scanner magnets,  
       a location-sensitive detector (MWPC 1 ) for location measurement, which is controlled by means of a control and read-out module (SAMO 1 ),  
       a sequence control device (VMEAS), which controls the activation and read-out sequence among the devices of the apparatus, and  
       wherein the method is characterized by the following steps: 
       comparison of information, deposited in the location measurement control and read-out module (SAMO 1 ) of a supervisory control system and relating to the desired position of the beam plan, with the actual measured position of the beam position from a location-sensitive detector, in real time,  
       determination of a correction value for the scanner magnet supply devices (MGN) of the grid scanner, and  
       setting the correction value for the horizontal and vertical magnet supply devices (X, Y) of the grid scanner and realignment of the beam position.  
     
     
       5. Method according to  claim 4 , characterized in that the realignment is carried out from beam position to beam position. 
     
     
       6. Method according to  claim 4 , characterized in that the realignment is carried out from measurement cycle to measurement cycle, the duration of a measurement cycle being shorter than the duration of a beam position. 
     
     
       7. Method according to  claim 4 , characterized in that, for each measurement cycle, real-time software in the control and read-out module (SAMO 1 ) of the location-sensitive detector (MWPC 1 ) calculates the actual value of the beam position from the detector data and sends that information by way of a data connection between the control and read-out module (SAMO 1 ) of the location-sensitive detector (MWPC 1 ) and the control and read-out modules (SAMS) for the scanner magnets. 
     
     
       8. Method according to  claim 4 , characterized in that, for a feedback control cycle, real-time software compares the desired position and the actual position of the beam position and calculates current-correction values for the horizontal and vertical magnet current supply device (GMN) of the grid scanner and sets the corrected current values. 
     
     
       9. Method according to  claim 4 , characterized in that beam realignment is carried out using damping that is arranged to be set by means of the real-time software in the control and read-out modules for the control magnet (SAMS). 
     
     
       10. Method according to  claim 4 , characterized in that rapid switching-off of the beam is triggered by the control and trigger module (SAMO 1 ) of the location-sensitive detector in real time if the difference between the measured value and the desired value of the beam position exceeds a threshold that is arranged to be set in the real-time software of the control and read-out module (SAMO 1 ) of the location-sensitive detector (MWPC 1 ).